The invention relates to alarm systems and particularly to acoustical glassbreak detectors. Acoustical glassbreak detectors typically include an omnidirectional microphone. For the purposes of this application the side of such microphones on which the microphone is most sensitive is referred to herein as the front and the opposite side of such microphones is referred to herein as the back. Known acoustic glassbreak detectors have experienced problems with false alarming in response to strong impacts to the surface on which the detector is mounted when the impact is at the back or behind the microphone element. This occurs in the CE Oak Beam Impact Test.
The prior art includes U.S. Pat. No. 5,192,931 issued on Mar. 9, 1993 to Richard A. Smith, the applicant herein, and Christopher A. Bernhardt. The disclosure of this patent is incorporated by reference herein.
The applicant herein was also issued U.S. Pat. No. 6,538,570 on Mar. 25, 2003. The present invention provides an improvement over the apparatus described therein. The apparatus in method described therein is highly effective. However, in some cases false alarms may occur as the result of an impact to the surface on which the microphone sensor on a part of that surface which is behind or opposite to the direction in which the microphone sensor is most sensitive.